The present invention relates to a method for making a fast transition of the entire superconducting winding of an electric apparatus which is disposed in a vacuum chamber and cooled by a cryogenic medium, from the superconducting operating state into the normal-conducting state by heating the entire winding in the event that at least one winding region which has been superconducting until then, becomes normal-conducting in the case of a disturbance. Such a method is known from the journal "Cryogenics", August 1979, pages 467 to 471. The invention further relates to apparatus for carrying out this method.
In large superconducting windings of electrical apparatus such as magnets or machines, very large amounts of energy can be stored, for instance, 10.sup.9 Joule. If, in the event of a disturbance, a limited section of the conductor of such a winding change from its superconducting operating state into the normal-conducting state, the danger exists that in this section of the conductor large amounts of energy are converted into the form of heat if normal conduction, also called quench, occurs, so that the conductor section melts through.
In the event of such a disturbance, the supplied energy must therefore in general not be converted locally since this can lead to the destruction of or damage to the winding unless suitable protective measures are taken. Among a number of possible measures, the fast removal of the energy into external parallel resistors is provided for large stabilized magnets. See, e.g., "Cryogenics", June 1964, pages 153 to 165. The removal of energy by inductive means is also known as a protective measure, see, e.g., "Cryogenics", December 1976, pages 705 to 708. The use of these measures, however, may result in technical insulation problems if the stored energies are very large.
It is well known that in the case of a conversion of the energy stored in large magnets into heat, uniformly distributed over the entire winding, the temperature rise connected therewith is relatively small, so that there is no danger of damage to the winding and therefore to the electrical apparatus containing it. If normal conduction occurs in an isolated region of the superconducting winding, one therefore endeavors to convert the stored energy not only in this region, but in the entire winding, by transferring the entire winding into the normal-conducting state as quickly as possible. According to the publication "Cryogenics", August 1979, mentioned above, special heating elements are built into the winding for this purpose, by means of which the entire winding can be heated up uniformly in the event of a disturbance. Arranging suitable heating elements in the winding, however, is relatively expensive and can likewise lead to technical problems with the insulation.
It is therefore an object of the present invention to provide an improved method and apparatus for causing a superconducting winding to make a fast transition to the normal-conducting state.